The present invention generally relates to a keyboard, such as a computer keyboard and a music instrument keyboard, and in particular to forming a switching circuit of a keyboard without generating phantom phenomenon.
A multiple switch keyboard, such as a computer keyboard and a music instrument keyboard comprises a plurality of switches. The arrangement of the switches generally falls in two categories. The first category comprises providing a switch for each input terminal wherein a plurality of switches is required for completing a switching circuit. A great amount of space is thus required for accommodation of the switches. Furthermore, such an arrangement is costly.
The second way of arranging the switches is forming a matrix. This substantially reduces the number of the switches that are required by the first method. The drawbacks related to the first arrangement are eliminated. However, the second arrangement suffers the xe2x80x9cphantom phenomenonxe2x80x9d which is caused by a reverse current resulting from simultaneous actuation of three switches among four switches arranged at four corners of a rectangle of the switch matrix.
To solve the problem of xe2x80x9cphantom phenomenonxe2x80x9d, diodes are added in the switch matrix for preventing the reverse current. The addition of diodes in the switch matrix leads to increase of costs.
Thus, it is desired to have a method for arranging switches in a keyboard switching circuit to prevent phantom phenomenon without substantially increasing costs.
Accordingly, an object of the present invention is to provide a method for forming a keyboard switching circuit without generating the phantom phenomenon.
Another object of the present invention is to provide a cheap arrangement of switches of a keyboard switching circuit for eliminating the phantom phenomenon.
To achieve the above objects, in accordance with the present invention, a method for forming a keyboard switching circuit without generating phantom phenomenon is disclosed. The method comprises the steps of (1) forming a matrix of nodes with input/output terminals of the keyboard circuit; (2) selecting nodes from the matrix to define a reference diagonal line which divides the matrix into upper and lower portions; (3) selectively selecting nodes of the matrix in the upper and/or lower portions to define diagonal lines parallel to the reference line, the diagonal lines being located at different distances from the reference lines and the nodes of the diagonal lines forming no rectangle with each other; and (4) setting switches in the selected nodes. Since no rectangle can be formed among the switches, no reverse current may be caused by simultaneous actuation of three switches of a rectangle and thus effectively eliminating the phantom phenomenon.